‘Now in my mind this is one of those things that is cool that is can be done but actually nobody would do for real unless maybe they lived on the Isle of Wight, and whats wrong with Google maps anyway’

We can think of a few good reasons why someone would want to do this.

First, you can (without getting sued) – OSM data is provided under a CC-by-SA license, so you can do what you want with it, so long as you attribute OpenStreetMap and you maintain the CC-by-SA license. The whole point of OSM is to allow people to do interesting things with data – like putting it on mobile phones, something which the Google Maps license forbids. Mobile application developers wont get a cease and decist from OSM.

If this is too niche, consider that OSM is current – OSM data is updated by over 15,500 volunteers, distributed across the world, realtime. If you make an edit to OSM data the changes are immediately available to anyone. There is no ‘validation layer’ and tiles served from openstreetmap.org are continuously re-rendered.

OSM data is richer than Google’s. OSM contains all manner of points of interest – pubs, car parks, shops and amenities – it even contains building outlines in some areas. Google’s data is largely limited to roads, some (not all) train lines and train stations.

Google’s maps are one-size-fits-all cartography. Google don’t produce cycling maps, countryside maps or other special interest products. OSM do, and as the richness of the dataset continues to improve and as the number of contributors to the project continues to rise, we are going to see more and more special interest products that fulfill a multitude of niche needs.

A few people will hack their iPhone to show OSM maps this year, probably for fun. But ultimately crowd sourced data like OSM’s is going to provide a richer, more current, global dataset than any closed source alternatives.

My first introduction to OSM was the SOTM conference; I thought it was an interesting idea, but was skeptical you could get decent results on a bike with a £150 GPS vs professional surveying equipment.

OSM’s map of Haywards Heath was literally just two main roads, so I thought it’d be a good opportunity to do a “first principles” look at what OSM involved and the kind of results it produced.

The first step was to build the map, after which I planned to go back and see how many mistakes I’d made (quite a few!) as well as measure how much effort it took to correct them.

After that, I thought it’d be useful to do a street-level comparison with another map to give some context to the OSM results.

Although comparing maps can open you up to charges of copying data, I’m absolutely behind the OSM model whereby if you ever upload data from a tainted source then your account and all its contributions are simply erased.

In a previous life I ported Windows games over to the Mac, so I am completely paranoid regarding IP ownership – if you’re responsible for source code that someone else spent a lot of time and money to create, you have to be!

As such I only map features for which I have a GPS trace or a geo-tagged photo, all of which are made public (traces in OSM, photos on flickr). Whenever I revisited an area to improve the OSM map, I captured a new trace and made improvements based on that trace.

2. What surprised you most about what you found?

I think the first thing that surprised me most was how easy it was to miss things.

Once I had completed the initial pass, I forced myself to go back with a printed OSM map to test just how accurate a single pass actually was. I honestly felt it would be a waste of time, as the map did look pretty complete.

However I kept finding the same kind of errors I subsequently noticed on Google Maps – streets would be in the wrong place, bad GPS reception meant I drew the wrong shape, names were swapped, stubs missed, etc.

The second thing that surprised me was that, apart from those minor errors, there weren’t really any major flaws.

The road network has pretty much the same shape as every other map, so a bike and a consumer-level GPS were easily accurate enough to capture it.

Fixing errors was also easier than I expected, although I think JOSM/Potlatch are probably still too technical for genuine “end user” changes.

As a programmer I found the download/edit/upload workflow very familiar (just like cvs/svn/etc), but I think a true mass market approach needs a “stick a pushpin on the map to file a bug report” model (where anyone can flag up bugs, and these go in a queue to be re-surveyed by someone more familiar with the project).

3. What will you do now you’ve mapped all of the roads, footpaths and pubs in your town?

There are other towns nearby which aren’t so well mapped, so there’s enough to keep me busy for a while.

I am also interested in the “completeness” aspect of OSM, as I think that’s one of the challenges the project faces. All maps are an approximation, but at what point do you say part of OSM is “done”?

For example, are there any tools/processes we could adopt which would help us communicate that kind of information to each other or to new users? Should we try and measure the quality/coverage of OSM data somehow, or find some way to indicate that on the map?

4. What do you think the impact of your work in Haywards Heath will be?

I’ve no idea – but it would be nice to think that someone will find it useful in the future.

For example, there’s a large town map at the train station which a commercial cartographer supplied to the council. That map states it was derived from out of copyright material and direct surveys, and it has a couple of errors relative to the OSM map.

It would be good if whoever created that map could just pull data from OSM in the future, as I think that kind of commercial usage will help improve the project’s visibility.

5. Is anything un-mappable?

Given sufficient resources, you can of course map anything.

Although OSM doesn’t currently capture all the things commercial data providers do (e.g., house numbers or turn restrictions), I don’t think there’s any fundamental reason to think it couldn’t.

OSM’s tagging model can capture most concepts, you can always buy a bigger disk/server, and the road network is stable enough that individuals can easily track changes (as I noticed doing Haywards Heath, some of the errors on Google Maps are at least 4 years old).

The limiting factor is going to be that it’s not very interesting to go out and write down house numbers or parking restrictions, so beyond the basic road network there may be some tasks that require more effort than you can expect from a voluntary project.

But those are all solvable problems, so I think the only areas that will be inaccessible in the future are things like nautical/aviation data. Simply because the resources you need to capture it are still out of reach of individuals, although that may not be the case forever.

Dair’s analysis makes for interesting reading. If you still doubt the utility of OSM data, ask yourself how much money your organisation could save by using and contributing to open geodata.

The most voiced criticisms about OpenStreetMap are that the data is not complete and that the data is not reliable. ‘Completeness’ and ‘reliability’ are relative measures; my map is more complete than yours for my personal definition of completeness. If your requirements for completeness are all the motorways in the UK, or the footpaths of London, or the rail network of the UK, or the Tube stations in London, then OpenStreetMap’s data will fit your needs.

The reliability argument goes like this; ‘How can I trust OpenStreetMap maps. They are volunteers on bikes with cheap GPS, Navteq have vans with expensive GPS.’ Fair enough?

OpenStreetMap volunteer, Dair Grant does not think so. After completing mapping his local town of Haywards Heath, he set about comparing the quality of OpenStreetMap’s data against that of Google Maps, supplied by TeleAtlas. The findings of his study can found here.

Dair found 89 errors in Google Maps, based on the elements that appear in both OpenStreetMap and Google’s Maps (Google do not include bridleways OSM do, for example). These included incorrect junctions, missing roads, incorrect geometries and roads that simply did not exist. To confirm that the ‘errors’ were not on the part of OpenStreetMap, Dair went back out and resurveyed the areas he had pinpointed as containing errors.

Dair’s work clearly demonstrates what most OpenStreetMap volunteers know already – that for areas where OSM’s data exists, it is usually of a high quality. Why would someone give up their free time to make a map and not do it properly? There are no ‘Friday afternoons’ or ‘lazy Mondays’ for volunteers – if you can’t be bothered, you just go home. Conversely, large companies spend massive amounts of money managing and motivating their staff and then making sure that their work is up to scratch.

Of course, volunteers can make mistakes too, but their motivations for revealing their mistakes are different to employees. There is little point in an OpenStreetMap volunteer covering up a mistake they made. All of OpenStreetMap’s data is open, so if you see a mistake in the map, you can access the raw data and fix it. Furthermore, many volunteers make their edits public, meaning that anyone can see the OSM name of the person who collected the data. You earn bad OSM points if the community catch you out. Compare this to the attitude of an employee of a large company. There is an entire management infrastructure dedicated to making sure the employee does their job properly. But unless that infrastructure is working 100% effectively, mistakes are going to slip through. And what is the point in the individual reporting their misspelling or wrong attribution of a road? Furthermore, what do you, the consumer do when the errors reach your rung on the supply chain? The large mapping companies have realised the potential for crowd sourcing data – but they are applying a thin layer on top of their system. They are allowing bug-reporting – they are not exposing the entirety of their software and hardware systems, mapping methodology and management techniques for the inspection of the world. This is why they are borrowing from the innovations of the open community and why the software and ultimately the data of the open community will be superior to that of proprietary producers.